The present invention relates to an electronic part such as a dielectric filter or duplexer, having a plurality of resonators arranged parallely in a row for use in a mobile communication device such as a portable telephone. The present invention further relates to a method of forming an electrode of such an electronic part.
A dielectric filter or duplexer is a known electronic part having a dielectric. In this connection, the dielectric duplexer has a dielectric ceramic block formed with a plurality of parallel through holes extending between the opposite end surfaces of the dielectric ceramic block. Each through hole has an inner conductor formed on an inner circumferential surface thereof and constitutes a resonator. The dielectric ceramic block has a predetermined outer peripheral surface on which an outer conductor is formed. The resonators are divided into two groups, i.e., a first group constituting a transmitting section and a second group constituting a receiving section. With the transmitting section is coupled an input terminal pad that is electrically separated from the outer conductor. With the receiving section is coupled an output terminal pad that is electrically separated from the outer conductor. Further, to a mounting surface of the dielectric ceramic block is provided an antenna terminal pad that is electrically separated from the outer conductor and capacitively coupled with the innermost conductors of the transmitting section and the receiving section. In such a duplexer, it is also known to form the output terminal pad on the side surface of the dielectric ceramic block and at a location adjacent the open-circuit end of one of the resonators constituting the receiving section so as to be opposed to the one resonator and form an extension electrode extended from the output terminal pad to the open-circuit end of the one resonator so as to be capacitively coupled with the resonators constituting the receiving section.
According to an earlier technology, the extension electrode at the open-circuit end of the one resonator is formed in the following manner. Firstly, ceramic powder is formed into a nearly rectangular parallelepiped compact having a plurality of through holes. At the time of the compact being so formed, the compact is also formed with an extension electrode-forming notch at an end surface corresponding to the open-circuit ends of the resonators of the receiving section so as to have an open end at the side surface of the dielectric ceramic block where the output terminal pad is formed. The compact is sintered to produce a dielectric ceramic block. Then, a plurality of dielectric ceramic blocks b are arranged in a row as shown in FIG. 7. Namely, the dielectric ceramic blocks b are arranged in such a manner that the surfaces on which the output terminal pads are to be formed are perpendicular to the direction in which the dielectric ceramic blocks are arranged in a row. When a plurality of dielectric ceramic blocks b are arranged in a row in the above-described manner, a recess e is formed by the extension electrode-forming notch c and the side surface of the adjacent dielectric ceramic block b. By supplying a conductive material in the form of paste into the recess e, the extension conductor d is formed. Then, the dielectric ceramic blocks b formed with the extension electrodes d are separated to obtained extension electrode-formed dielectric ceramic blocks axe2x80x2. The outer conductor is formed on the outer peripheral surface of the extension electrode-formed dielectric ceramic block axe2x80x2 except for an open-circuit end surface and predetermined side surface portions. The input terminal pad, etc. are formed on the extension electrode-formed dielectric ceramic block axe2x80x2 so as to be electrically separated from the outer conductor. In the meantime, the output terminal pad is formed on the side surface of the extension electrode-formed dielectric ceramic block axe2x80x2 so as to be electrically connected to the extension electrode d.
However, the above-described electrode forming method has the following problem.
Namely, as shown in FIG. 7, when the conductive material is supplied into the recess e, the surface of the conductive material is U-shaped in cross section due to surface tension, i.e., shaped so as to have surface portions that rise up or extend upward along the side surfaces of the dielectric ceramic blocks b. Accordingly, the electrode d formed in the recess e has a largest thickness hxe2x80x2 portion on the side surface k of the adjacent dielectric ceramic block b. When the dielectric ceramic blocks b are separated under this condition, the electrode d is broken and taken away together with the separated dielectric ceramic block b as shown in FIG. 8A. Further, as shown in FIG. 8B, there occurs another case in which a burr dxe2x80x2 is caused. Such a problem is also caused in an electronic part such as a dielectric filter.
It is accordingly an object of the present invention to, provide an electronic part such as a dielectric filter or a dielectric duplexer that is free from the above noted problem.
It is a further object of the present invention to provide a method of forming an electrode of an electronic part of the above-described kind that is free from the above noted problem.
To achieve the above object, there is provided according to an aspect of the present invention an electronic part comprising a dielectric ceramic block having a pair of opposite first and second side surfaces and an end surface meeting the first and second side surfaces nearly at right angles, a first notch formed in the end surface of the dielectric ceramic block so as to have an open end at the first side surface, a second notch formed in the end surface of the dielectric ceramic block so as to have an open end at the second side surface, the first notch and second notch corresponding in shape and position when observed in the direction in which the first and second side surfaces are opposed, a first electrode formed in the first notch, and a second electrode formed in the second notch, the second electrode being a dummy electrode.
According to another aspect of the present invention, there is provided a method of forming an electrode of an electronic part, the electronic part including a dielectric ceramic block having a pair of opposite first and second side surfaces and an end surface meeting the first and second side surfaces nearly at right angles, a first notch formed in the end surface so as to have an open end at the first side surface and a first electrode formed in the first notch, the method comprising the steps of preparing a dielectric ceramic block having in addition to the first notch a second notch formed in the end surface of the dielectric ceramic block so as to have an open end at the second side surface and correspond in shape and position to the first notch when observed in the direction in which the first and second side surfaces are opposed, arranging a plurality of dielectric ceramic blocks in a row so that the first notch and the second notch of adjacent two of the dielectric ceramic blocks are joined to form a recess, supplying a conductive material into the recess and forming the first electrode and a second electrode that is a dummy electrode, and separating the dielectric ceramic blocks and thereby separating the first electrode and the second electrode of adjacent two of the dielectric ceramic blocks from each other.